BONE MORPHOGENETIC PROTEIN-2 INHIBITS TERMINAL DIFFERENTIATION OF MYOGENIC CELLS BY SUPPRESSING THE TRANSCRIPTIONAL ACTIVITY OF MYOD AND MYOGENIN

Bone morphogenetic protein (BMP) is a family of cytokines that induce ectopic bone formation when implanted into muscular tissues. We report ed that BMP-2 inhibits the terminal differentiation of C2C12 myoblasts and concerts them into osteoblast lineage cells (Katagiri, T., Yamagu chi, A., Komaki, M., Abe, E., Takahashi, N., Breda, T., Rosen, V., Woz ney, J. M., Fujisawa-Sehara, A., and Suda, T. (1994) J. Cell Biol. 121 , 1755-1766). In the present study, we examined the molecular mechanis m of the inhibitory effect of BMP-2 on terminal differentiation of myo genic cells. When either MyoD or myogenin cDNA was introduced into C3H 10T1/2 (10T1/2) cells with a muscle-specific CAT reporter containing f our copies of the right E-box of muscle creatine kinase (MCK) enhancer , the CAT activity was dose-dependently suppressed by BMP-2. Furthermo re, BMP-2 inhibited the terminal differentiation of these subclonal 10 T1/2 cells that stably expressed MyoD or myogenin into mature myotubes that expressed myosin heavy chain and troponin T. The differentiation of a subclone of the MyoD-transfected NIH3T3 cells into mature muscle cells was also inhibited by BMP-2. BMP-2 induced alkaline phosphatase activity in 10T1/2-derived, hut not in NIH3T3-derived MyoD-transfecte d cells. These cells constitutively expressed exogenous MyoD and myoge nin, which were localized exclusively in the nuclei irrespective of th e presence and the absence of BMP-2. However, these cells failed to ex press the mRNAs of endogenous myogenic factors and MCK when cultured w ith BMP-2. In the electrophoresis mobility shift assay using nuclear e xtracts of the myogenic cells, MyoD and myogenin bound to the right E- box in the enhancer region of the MCK gene even in the presence of BMP -2. These results suggest that BMP-2 inhibits the terminal differentia tion of myogenic cells by suppressing the transcriptional activity of the myogenic factors. (C) 1997 Academic Press.